The present invention relates generally to the field of magnetic data storage and retrieval. In particular, the present invention relates to a high frequency writer having a sliced core topology to minimize eddy current effects in the writer core.
A typical magnetic recording head consists of two portions: a writer portion for storing magnetically-encoded information on a magnetic disc and a reader portion for retrieving that magnetically-encoded information from the disc. The reader typically consists of two shields and a magnetoresistive (MR) sensor. positioned between the shields. Magnetic flux, from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
The writer typically consists of two magnetic poles, or a magnetic core, separated from each other at an air bearing surface of the write head by a write gap and connected to each other at a region away from the air bearing surface by a back via. Positioned between the two poles are one or more layers of conductive coils encapsulated by insulating layers. The writer and the reader are often arranged in a merged configuration in which a shared pole serves as both a shield in the reader and a magnetic pole in the writer.
To write data to the magnetic media, a time-varying electrical current, or write current, is caused to flow through the conductive coils. The write current produces a time-varying magnetic field in the magnetic poles. The magnetic field bridges the write gap forming a write gap field. The magnetic media is passed over the air bearing surface of the writer at a predetermined distance such that the magnetic surface of the media passes through the gap field. As the write current changes, the write gap field changes in intensity and direction.
As the write gap field changes directions, a counteracting flow of current is induced in the magnetic core. This induced current, which is known as an eddy current, attempts to oppose or reduce the change in magnetic flux. Eddy currents have a negative effect on the performance of the magnetic recording head. First, the eddy currents act as a shield to prevent external fields from penetrating the magnetic core, thereby reducing the efficiency of the recording head. Second, the eddy currents hinder the propagation of magnetic flux through the magnetic core, thereby causing a delay in the rise of magnetic flux at the writer gap. This increases phase lag between the magnetic flux and the magnetic field fringing out at the writer gap reduces the efficiency of the magnetic recording head.
As the frequency of the write current through the recording head increases to allow for increased data storage rates and densities, eddy currents have even more pronounced effects. It is well known that the inefficiency of the magnetic recording head increases in proportion to the square of the operating frequency. Accordingly, there is a need to reduce the occurrence of eddy currents in the recording head""s magnetic core.
One common prior art attempt to reduce eddy current effects is to increase the resistivity of the material forming the magnetic core. Higher resistivity materials, however, generally have lower saturation moments, which result in the recording head having a reduced efficiency. Additionally, recording heads made of lower saturation moment materials are not capable of recording on higher density recording media.
A second common prior art approach to reducing eddy current effects is to form the core of horizontal laminations of thin films which alternate between thin films of traditional core materials and thin films of electrically insulating materials. However, the choice of a multi-layer lamination for the core will increase manufacturing costs because sputtering, rather than plating, technology must be employed for the deposit of traditional core materials on electrically insulating materials.
Accordingly, there is a need for a new method of reducing eddy current effects in a writer core to allow for a cost-efficient, high frequency writer.
The present invention is a high frequency recording head having a sliced core topology which reduces the effects of eddy currents in the recording head. A magnetic recording head of the present invention has an air bearing surface and a magnetic core having a height and a width. The magnetic core is formed in part of a plurality of narrow slices having a plurality of insulating channels interspersed therein along the width of the magnetic core. Each of the plurality of narrow slices extends essentially along the height of the magnetic core.
In a preferred embodiment of the present invention, the magnetic core is formed of a top magnetic pole and a bottom magnetic pole. Each of the top and bottom magnetic poles has an air bearing surface and a back surface opposite the air bearing surface. The bottom magnetic pole is separated from the top magnetic pole at the air bearing surfaces by a write gap, and is in contact with the top magnetic pole at the back surfaces. In the top magnetic pole, each of the plurality of insulating channels extends from the back surface of the top magnetic pole toward the air bearing surface of the top magnetic pole. Similarly in the bottom magnetic pole, each of the plurality of insulating channels extends from the back surface of the bottom magnetic pole toward the air bearing surface of the bottom magnetic pole.